Presently, the design and layout of an optical integrated circuit requires the assistance of an expert circuit designer, which is often a waveguide physicist who is also a highly experienced programmer. The expert designer is presented with a task of designing and laying out an optical circuit that provides certain functionalities. For instance, the expert designer may be presented with the task of designing a certain Mach-Zehnder interferometer that has a certain response at a particular wavelength.
One of the first steps in the design of an optical circuit is the determination of the circuit's defining parameters. For a Mach-Zehnder interferometer, one of these parameters would be the difference in path lengths between the two arms of the Mach-Zehnder interferometer. To find the proper values for the parameters of a circuit, the expert designer must write a program, such as a Fortran program, that provides a spectral analysis for the desired circuit. In the example of the Mach-Zehnder interferometer, the expert designer would write a program that would provide a spectral analysis of the Mach-Zehnder interferometer at the specified path difference. The expert designer could therefore verify the operation of a particular optical circuit having certain specified dimensions and parameters.
Once the dimensions and parameters for the optical circuit are known, the expert designer next writes a second program for laying out the optical circuit. This second program provides an x-y plot by which a fabricating machine, such as a photolithographic machine, can lay out a desired mask. The mask which is defined by this second program must be very accurate in specifying path lengths and must be able to define various curves in order that the optical circuit perform as desired.
More specifically, one manner in which the second program defines the mask of the optical circuit is by selectively calling a number of subroutines from a library of subroutines. In general, each of the subroutines in the library defines a unique structure. For instance, one subroutine might define a curved bend between two points with a certain radius of curvature and a certain width. An entire set of subroutines might be necessary to define the various portions and structures of a Mach-Zehnder interferometer. The second program selectively calls these subroutines and provides the subroutines with the necessary data or parameters to define the desired optical circuit.
The design and layout of the optical circuit is an extremely complex and involved process. Since the process requires the expertise of one skilled in waveguide physics as well as in computer programming, only a relatively small and select group of people are qualified to design and layout an optical circuit.
The process of designing and laying out an optical circuit is also a rather lengthy process and frequently takes as long as a month. One reason for this long overall design time is that the expert designer or team of designers must write, as well as debug, two different programs for each optical circuit that they design with one program providing a spectral analysis and the other program defining the mask layout. While the programs for another optical circuit may be derived from an existing set of programs for a similar circuit, the programs for the other circuit are nonetheless unique and must be written and debugged for the new circuit. For instance, a Mach-Zehnder interferometer having the same dimensions would still require different programs even if the only difference between the two devices was the index of refraction for the substrate material.
Another challenge facing the expert circuit designer is that a substantial amount of data must be tracked during the design and layout of an optical circuit. Each optical component in an optical circuit is defined by a number of parameters, such as length of waveguides, path difference between waveguides, separation between waveguides, radius of curvature in the waveguides, etc. The large number of parameters for each optical component therefore renders the process of writing the programs for both the spectral analysis and layout of an optical circuit extremely exacting.
A further challenge facing an expert optical circuit designer is the ability to visually verify an optical circuit. During the mask layout phase of the circuit design, the contours of the circuit is defined by a set of coordinates. Due to the large number of coordinates, the exact relationship between the coordinates is not readily apparent from studying the coordinates. To provide a visual confirmation of the circuit, a graphical editor program may be employed. The graphical editor program connects the various points in the mask layout and forms shapes and contours which together provide a visual image of the optical circuit. Since a visual confirmation of the optical circuit does not occur until after the expert designer has written and debugged two programs, the expert designer must exert a substantial amount of time and effort before receiving visual confirmation of the desired circuit.
The challenges facing the expert designer do not stop at the circuit level but are also prevalent at the chip and wafer level. Once the individual circuits have been designed and laid out, the expert designer must additionally write and debug programs to combine the circuits onto a chip or to combine various chips onto a single wafer. These programs will, inter alia, add the various labels and markers on the wafer relied upon in the fabrication of the chips.
In the electrical arts, one skilled in the art is provided with computer-aided design (CAD) tools for designing and laying out electrical circuits. In the development of the electrical CAD tools, an expert circuit designer would design and layout building blocks of electrical circuits, such as AND gates, OR gates, and multiplexers, on the transistor level for a particular technology, such as 0.5 micron CMOS. One familiar with the functions of these elements could then use the CAD tool to selectively combine the basic building blocks to form a desired electrical circuit. The electrical CAD tool would additionally generate a mask layout for the various semiconductor devices.
The design of optical circuits, in contrast to electrical circuits, has considerations which cannot be directly translated from the electrical arts. For instance, the length and shape of an optical waveguide plays a much more significant role on the proper functioning of the circuit than the length and shape of an electrical conductor. A sharp bend in an optical waveguide can introduce an unacceptable loss in signal whereas in the electrical arts, an electrical conductor is commonly laid out with ninety degree bends and is not rendered inoperable simply by the shape of the conductor. Thus, the underlying physics of optical signals and optical circuits prevent the simple translation of an electrical CAD tool into an optical CAD tool.
Another difficulty in the design of optical circuits is that the planar waveguide technology is still evolving and key waveguide factors related to process parameters are not fixed. With each change in technology, such as a change in substrate material, the programs for an optical circuit must be at least modified and debugged. Thus, even if a CAD tool was developed for a single technology, the CAD tool would soon become outdated when new technologies were developed.
The availability of new optical circuits is becoming of more and more significance as the technology is shifting from electrical communication to optical communication. An impediment to this transition from electrical to optical is the cost of optical technology, which is highly dependent upon the number of interconnects between optical devices. Since the cost of the optical devices can be drastically reduced by integrating existing optical devices onto a single substrate, thereby reducing the number of interconnects, a number of new optical circuits will have to be designed. In order to expedite this transition, the expert designer must be able to reduce the overall time needed to design and layout an optical circuit.
In summary, a need exists for a system or process which can assist in the design and layout of an optical circuit. Moreover, a need exists for a system or method which can significantly reduce the amount of time needed to design and layout a circuit and one that can greatly simplify the process whereby one, who is neither a waveguide physicist or a programmer, can design and layout an optical circuit. A need also exists for a system or method which can provide a designer with a visual confirmation of the desired circuit at various stages throughout the design process. Furthermore, a need exists for a method or system which can assist in the design of an optical circuit for various types of technologies, as well as for technologies embodying future advances.